Hematology, Histopathology and the Monogenean Neoheterobothrium hirame Infection in Anemic Flounder

Abstract

Recently, severe anemia of unknown etiology has been observed frequently in both wild and cultured Japanese flounder, Paralicthys olivaceus, in Japan. Hematological and parasitological examinations and histopathlogical examinations on the hematopoietic organs were carried out in anemic flounder. The anemia was hematologically characterized by the appearance of many immature erythrocytes and abnormal staining in the cytoplasm (vacuolation or weak staining) of erythrocytes. Histopathologically, deposition of hemosiderin or necrosis was rarely observed in the kidney or spleen of the anemic flounder. The blood-feeding monogenean, Neoheterobothrium hirame, was observed at high prevalences in flounder groups in which many anemic fish were contained. These observations suggest that the anemia was caused by the hematophagia by the parasite.